DIFFERENCE IN CHROMATIN PACKAGING BETWEEN ACTIVE AND INACTIVE X-CHROMOSOMES BY FRACTIONATION AND ALLELE-SPECIFIC DETECTION

Using a novel method consisting of chromatin fractionation and allele- specific detection, chromatin packaging is compared between active X ( Xa) and inactive X (Xi) chromosomes for five tumor cell clones that we re derived from inter-subspecific F-1 female mice, Separation of heter ochromatic (H) and euchromatic (E) fractions is monitored by hybridiza tion with subtelomeric satellite DNA and ribosomal RNA gene and by PCR amplification of p53 gene/pseudogene with one primer set. The H fract ion was enriched with satellite and p53 pseudogene probably existing i n heterochromatic regions while the E fraction showed inverse, suggest ing fair separation. Analysis with seven marker and three gene loci re vealed concentration of alleles on Xi in the H fraction and those on X a in the E fraction, though the concentration levels varied, This impl ies that the packaging level of Xi is higher than that of active or in active euchromatin on Xa. Intriguingly, one cell line showed biallelic expression and chromatin relaxation of the Pgk-1 locus, suggesting th at the relaxation occur regionally on X chromosome. (C) 1998 Academic Press.